The manufacturing process of semiconductor devices is interlaced with testing and inspection operations. While many of these testing and inspection operations involve direct human interaction with the manufactured device, a large percentage of these testing operations are automated. That is, a machine will sequentially test each of a series of devices to determine whether each individual device is satisfactory or unsatisfactory, and identify the satisfactory devices from the unsatisfactory (reject) ones. Reject devices which are physically separate from other devices can be physically placed in a reject pile. However, where the devices are connected together as, for example, semiconductor dice on a wafer, or bonded semiconductor die on a lead frame assembly consisting of a plurality of bonded devices, immediate physical separation is generally not practical and a marking method for later identifying unsatisfactory devices must be utilized.
One method for marking used extensively in the semiconductor industry on wafers is the use of an ink dot to visually mark reject die on a wafer. The inking method is fairly inexpensive and does not disturb adjacent semiconductor dice. However, the ink has a disadvantage of either being easily smeared or requiring a baking in an oven to set the ink. While these drawbacks are minimal in the wafer processing area, they can become significant in the area of marking defective semiconductor die which are bonded to lead frame assemblies.
Obviously baking ovens involve additional cost to procure and operate, and the bonded assemblies are too large and bulky to conveniently fit in a modest size oven. Other methods of marking such as punching a hole in the metallic lead frame and hand marking have been considered. However, punching produces the risk of disturbing adjacent good devices, and hand marking can place the operator's hand into the vicinity of moving machinery thereby creating a work hazard.
Thus, it can be appreciated that a method of marking articles of manufacture which is inexpensive, indelible, safe, and doesn's disturb adjacent good devices is highly desirable.